Most believe that more should be done to stop subjects unsuitable for children being broadcast at times when they are likely to be listening, and 85 per cent say daytime swearing should be banned.

The figures were revealed in a report, called Listening 2000, published by the Radio Authority and the Broadcasting Standards Commission.

A 17-year-old youth, of Southampton, was quoted in the report as saying: "One of the little kids at play school was saying 'bitch, bitch, bitch' and he called his mum a bitch, which he has never ever done again. Kids do pick up these words even if they don't know what they mean."

A middle-aged woman from London said she was embarrassed at having to explain a sexual term to her child after it was mentioned on the radio. "[Children] know when something's not right so they will ask me. I have questions about all sorts of things - 'what's a prostitute, what's a madam?' etc - because they have heard it on the radio," she was quoted as saying.

Launching the report, Martin Campbell, the director of programming and advertising of the Radio Authority, said: "Some of the interesting findings were the reasons given by the respondents who took offence. Almost half the number of people we spoke to felt offended at certain things they heard recently. Of those, a third switched off and a third switched over."

The report is published amid controversy surrounding high-profile radio disc jockeys such as Chris Evans and Zoe Ball.

The report said adults also took offence on their own behalf, with many criticising the harsh way presenters treated phone-in callers. About 15 per cent of respondents said this was the cause of their upset, while 14 per cent cited bad language, 7 per cent blamed sexual innuendo and 7 per cent said explicit or controversial song lyrics concerned them.

On a positive note, the report showed listeners were becoming more sophisticated as they adapted to the increasing choice of stations, saying they are becoming more willing to retune in search of "quality".